Thermoelectric conversion has long been known and generally recognized as affording the prospect of important advantages as a source of electric power, particularly in the form of lightweight, multi-fuel power generators. It has also been known for decades that the semiconducting compound lead telluride (PbTe) is the most efficient thermoelectric material for power generation in the temperature range of major interest from 125.degree.-550.degree. C. The bright promise of this technology in practical application has, however, never been realized. Thus, all the efforts made heretofore to improve the efficiency of thermoelectric conversion elements have resulted in only a marginal gain in that all-important quality as measured by the so-called "figure-of-merit Z", defined as: EQU Z=S.sup.2 /pK
where S is the Seebeck coefficient, p is the electrical resistivity, and K is the thermal conductivity of the thermoelectric material.